Method of cold-working metallic bars



atentecl May f2, 1944 Gerald G. Greulich, Mount Lebanon, Pa. ApplicationJuly 26, 1941, Serial No. 404,244

4 Claims.

The present invention relates to improvements which, while not limitedthereto, are peculiarly well suited for cold-working steelbars such asare utilized for concrete reinforcements.

Broadly stated, the invention comprises the steps of reversely bending abar throughout its full length while advancing it longitudinally througha series of alternately staggered pairs of rolls so as to cold-Work andstretch or compress the outermost bers and subsequently partiallyrotating the bar substantially or approximately about its longitudinalaxis and repeating said continuous reverse bending operations.

The above and morevdetailed features of the invention will be fullyapparent from the following detailed disclosure when read in connectionwith the accompanying drawing and the features of patentable noveltywill be defined with particularity in accordance with the requirementsof the patent statutes in the appended claims.

In the drawing: l

' Figure 1 diagrammatically illustrates a series of roll stands arrangedto reversely bend the bar at spaced points while the same is advancedlongitudinally through the undulating active pass 'defined by the rollsof the stands;`

Figure 2 represents a transverse section on line II--II of Figure 1through the work in the process of reverse bending operation;

Figure 3 is a View similar to Figure 2 but illustrating the condition ofthe bar in a second series of roll stands before it has been cold-workedby the rolls illustrated;

Figure 4 is a detail section diagrammatically illustrating by means ofcontrasted cross hatching the result of the cold-working operation towhich thek bar is subjected as shown in Figures 2 and 3; l

Figure 5 is a view similar to Figures 2 and 3 but illustrating by-thecontrasting cross hatching the condition of the fibers of the bar afterthe same has been subjected to more than one pass;

Figure 6 is a plan view-of the bar'shown in Figure 5; si

Figure 7 is a yiew similarto Figure 5il1ustrating by the contrastingcross hatching the effect of subjecting a substantially square bar to amul-- tiplicity of reverse bending operations; and

Figure 8 is a plan view of the bar shown in section in Figure 7. l

Referring in detail to the drawing, Figure 1 represents in cross sectiona plurality of roll stands in which the upper rolls` I0, I2, I4, I6, I8,and 22 cooperate with a plurality of lower rolls r1, ls, is, n, I9, 2|.andas to denne an ,undulatf ing active pass, the effect of which is toreversely bend the bar B fed therethrough throughout its full length asthe work progresses through the pass. The relationship of the rolls I Iwith respect to the rolls I0 and I2 is such that as the work enters itwill rst be subjected to a comparatively small bending operation. As itprogresses to the zone of the pass dened by the rolls I2, I3 and Ill, agreater bend will be made. Thereupon as the work proceeds through thatpart of the pass defined by the rolls I3,- I4 and I5, the work Will bebent inthe opposite direction. Thereafter as the rolls I4, I5 and I6come into play a bend of greater magnitude will be made. The work thenpasses to the rolls I6, Il and I8 Where it is reversely bent, but to alesser degree. Likewise the rolls Il, I8 and I9 will bend the work in adirection opposite to the bend effected by the immediately precedingrolls.v In this manner the work will progress through the rolls I8, I9and 29 and thence will be acted upon by the rolls 20, 2|, 22 and 23.

The effect of such progressive reverse bending operation` on thelongitudinally advancing work is to subject the outermost fibers of thebar stock to a cold-Working operation which strains and stretches orcompresses them nearly to the point approaching the ultimate strength ofthe material. As a result of such working, the outermost bers becomehardened, yet the inner bers in the central zone near the neutral axisremain substantially unworked. Thus the central bers are kept in anunhardened and ductile state.

In Figure 2 the result of the work hardening of the outer fibers has,been diagrammatically indicated by the more dense cross hatchingindicated at 24 and 26.v The bar illustrated in Figure 2 is ofapproximately octagonal contour in cross section. The conditionillustrated is that of a bar which has been passed through an undulatingactive pass formed by a series of offset rolls such. as illustrated inFigure 1. After the operation shown in Figure 2 the bar will be turnedapproximately 90 on its longitudinal axis to the position of Figure 3.Thus the densely hatched parts 24 and 26 of Figure 3 correspond with thesame parts similarly hatched in Figure 2. The work rolls shown in Figure3 may be regarded as the rolls I 0 and II. Thus the condition of the barin Figure 3 at the start of the operation is such that the eiectivelycoldworked portions are the heavily hatched portions. After this bar ofFigure 3 has passed through the active pass defined by the remainingrolls I2 to 23, inclusive, the upper and lower portions 28 and 30 ofFigure 4 will be coldworked as indicated .by the lmore dense crosshatching. Thus it is apparent that after the bar has been subjected tothe passes suggested by Figures Zand 3, substantially all of the outerzone thereof will have been subjected to cold- Working, and the outerfibers represented by the heavier hatching of Figures 5 and 7 will allhave the material, with a consequent increase in hardness and strength.

While the invention is not limited thereto, the described method ispeculiarly well suited for the treatment of concrete reinforcing bars.Such barsI are conventionally provided with ribs or protrusions such asindicated at 32. Figures 1 through 6 illustrate the invention as appliedto the working of a so-called octagonal bar. The same method may beapplied to the cold-working of a bar which is substantially square incross section but having its corners rounded. Figure 7 diagrammaticallyillustrates such a cornerrounded square bar in the process ofproduction. Figure 8 is a plan view of the rounded bar, Figure 7,showing the conventional ribs or protrusions 32 formed thereon. .Barssubjected to the improved method described will have their outer fibersall cold-worked and hardened a maximum amount while the central portionthereof in the zone of the neutral axis will be relatively soft andductile, The result of the treatment is that the bar will becharacterized by a high elastic limit due to the cold-working of theouter bers while at the same time it will have high ductility because ofthe relative softness of the center or neutral axis zone.

The advantage of the disclosed process is that a bar typical of manyreinforcing rods in demand today can be processed on conventional typesof mills. This is important because it permits of feeding loose barscontinuously end to end into the reverse bending rolls which results inextremely high speed processing. No handling of individual bars andfastening their ends to twisting or stretching machines or a combinationof both is required as heretofore.

The method provides for effectively endowing bars with-the desirablecharacteristics of coldworked high tensile or high yield point bars at avery low cost of production, and accompanying the high tensilecharacteristics the bar will be characterized by such a degree ofductility that it cari be readily bent to suit installationrequirements.

It is believed that the cold-working eiect or the raising of the elasticlimit and ultimate strength of the bar is eiTected by the speed of-'operation as well as by the magnitude of the reverse bends impartedwhile thebar is passing through the undulating pass defined by the rollsl0 to 23, inclusive. That is, with a relatively high speed, the samedegree of cold-Working can be obtained as that which could be obtainedby A been strained nearly to the ultimate strength of l tions heavily,then cold-bending such portions a. greater relative offsetting of therolls with respect to one another at a lower speed.

While the invention has been described with particular reference to thecold-working of concrete reinforcing bars, it will be understood that itmay have other applications. Accordingly, the drawings and descriptivematter are to be interpreted inan illustrative rather than a limitingsense since various modifications may be made by those skilled in theart without departure from the scope of the invention as set forth inthe appended claims.

I claim:

l. The method which comprises' advancing a bar longitudinally whilesubjecting successive portions thereof -to transverse bendings whichgradually increase and then gradually decrease in magnitude, whereby theouter fibers of the bar are stressed to a point approaching the ultimatestrength of the material While the intermediate bers in the region ofthe neutral axis are maintained relatively ductile, rotating the bar afraction of a revolution, and repeating the above steps on differentparts of the bar until all peripheral portions of the outer skin regionthereof are eectively hardened sequentially in separate stages.

2. The method which comprises advancing a bar longitudinally Whilecold-bending successive portions slightly, then cold-bending suchporslightly whereby the outer bers thereof are work-hardened.whi1e theintermediate fibers in theregion of the control axis are maintainedrelatively ductile, rotating the bar less than a half revolution, andrepeating the abovesteps until all peripheral portions of the outer skinregion of the bar are effectively hardened se= quentially in separatestages by said cold working.

3. The method of cold-working a steel bar which comprises advancing thebar longitudinally along an undulating path while sequentiallycold-bending the same transversely in varying increments which rstgradually increase and then gradually decrease in magnitude, rotatingthe bar a fraction of a revolution, and repeating the above steps ondifferent parts of the bar until all peripheral portions of the outerskin region thereof are effectively work-hardened'sequentially inseparate stages.

i 4. The method of cold-working a steel bar of polygonal cross-section,which comprises advancing the bar longitudinally while subjectingsuccessive portions thereof to transverse cold-bend-Y ing operationswhich first gradually increase and then gradually decrease in magnitude,rotating the bar approximately and repeating-the said steps until allperipheral skin portions of the bar are hardened sequentially by coldwork while the region in the zone of the neutral axis is maintainedrelatively ductile.

i GERALD G. GREULICH.

